1. Field of the Invention
The present invention relates to a polymeric injection mold for producing re-entrant molded surfaces and more particularly to a molding process and device for producing a molded article having re-entrant surfaces.
2. Description of the Prior Art
Many patents address issues related to injection molding of polymeric articles. The patents and publications that relate to polymeric injection molding with re-entrant surfaces are discussed hereinbelow.
U.S. Pat. No. 3,910,748 to Kopernik discloses plastic mold construction in which foamed thermoplastic articles, particularly elongated boards can be produced at a high rate of production. The mold may be selectively provided with different ornamental surface designs. The mold comprises a stationary match plate member and one or more movable plate members arranged for cooperation with the stationary match plate. One or more elongated ejector bars are slidably arranged to extend the entire length of the stationary match plate and when retracted within the stationary plate, an edge of ejector bar serves as part of the mold. Coordinated impact means dislodge the molded part from adherence to the ejector bar. When the board-like member is provided with an undercut, one or more rabbet mold parts are provided for selective but rigid securement during production by simple clamp means, to the stationary match plate. The disclosure is for elongated boards with ornamental surfaces. There is no disclosure of a mold construction for molding of polymeric articles with re-entrant surfaces.
U.S. Pat. No. 4,362,291 to Fuke et al. discloses a metal mold for molding a hollow article having inwardly tapered sidewall. The metal mold has a stationary bottom die plate, a core and a cavity plate surrounding the core. The core has a truncated pyramid shape and first and second slide cores are provided between the core and the cavity plate. The core and slide cores are constructed such that at the time of opening the mold both slide cores are moved inwardly in an interlocked relation, with retractive movement of the core thus enabling removal of the molded product. The metal mold is for molding a hollow article having inwardly tapered sidewall. The polymer is injected from the stationary bottom die. The hollow polymeric part has re-entrant surfaces defined by the cores. Several pin mechanisms as well as sliding elements have to move cooperatively to move the cores away so that the molded part can be removed. The mold requires a large number of parts to move cooperatively. In this invention, the re-entrant surface is entirely within the movable part of the die set. No re-entrant surfaces are present in the stationary part of the mold.
U.S. Pat. No. 4,495,135 to White discloses a method for forming a container having a re-entrant flange. A unitary, thermoformed container having an undercut or re-entrant seal flange is provided. The container is made in a molding method and apparatus in which a flange-forming portion has a short-stroke gate assembly that opens after the unitary, thermoformed container has been formed in order to provide an exit path away from the molding cavity to permit ready removal of the thermoformed container out of the molding cavity and its flange-forming portion. This method uses a short-stroke method for forming a thermoformed unitary container with undercut flange by longitudinally moving a web of thermoformable material over an undercut flange-forming member with a movable leading end that is at the upstream end of the molding cavity. The container is thermoformed with re-entrant undercut flange. The leading end of the molding cavity flange-forming member is opened and the body forming member and leading end forming member are separated. This is a thermoforming process of a sheet of polymer and is not an injection molding machine. The re-entrant flange is present in only one side of the separation line.
U.S. Pat. No. 4,678,158 to Brock discloses an injection mold including mold sidewall locking bars. The injection mold assembly includes a plurality of locking bars for securing the mold sidewalls in a closed position of the mold. The locking bars project from one mold plate and are positioned outwardly of the mold sidewalls and include ends adapted to engage the other mold plate when the mold is closed and to function as wedges preventing outward movement of the mold sidewalls. The first and second molding plates are locked by sidewalls when the mold is closed preventing their movement when the polymer is injected. There are no re-entrant surfaces in the mold.
U.S. Pat. No. 4,731,014 to VonHoldt discloses a rear opening mold. An injection mold comprises a cavity member and a core member relatively movable between open and closed positions to define a first parting line and a molding chamber between the core and cavity members in the closed position. A sprue aperture is provided, communicating with the molding chamber to provide molding compound to the chamber. The cavity member defines forward and rearward portions movable between open and closed positions and proportioned whereby objects molded in the molding chamber can be removed from between the forward and rear portions when the cavity member is in its open position. The '014 patent discloses a rear opening mold. In operation, the right side of the mold must be moved in order to collapse the outer core member. There is only one re-entrant edge facing the right side of the mold and none facing the left side of the mold. As a result, one side of the mold could be moved upon release of the outer core. The arrangement of the '014 invention requires a large number of actuation mechanisms to operate together to produce the polymeric molded part.
U.S. Pat. No. 4,854,849 to Sudo discloses an injection mold. The injection mold is provided for molding an article with an undercut at one end portion. The movable half of the mold has a slide core, which defines the inner surfaces of the end portion and the undercut. The slide core is divided at the portion defining the inner surfaces of the end portion and the undercut into a plurality of pieces. The slide core is moved in a direction perpendicular to the ejecting direction when the molded article is ejected from the mold. At least one of the pieces is adapted to be slid along an inclined surface, which is at an angle to the ejecting direction larger than the angle at which the inclined surface or surfaces for the other piece or pieces are to the ejecting direction. The molded part has only one re-entrant surface and is accommodated by the sliding movement of the core. The molded part does not have two opposing re-entrant surfaces from the parting line.
U.S. Pat. No. 5,252,057 to Landstorfer discloses an apparatus for ejecting moldings from an injection molding machine. An apparatus for ejecting a molding from an injection molding machine includes a linearly moveable ejector plate. The ejector plate has a reciprocatingly movable coupling device for connecting the ejector plate to a mold ejector plate in a form-locked and force-locked manner. The ejector plate also has a hydraulic cylinder having a movable coupling piston connected to a coupling rod. This coupling rod has a head end, which is insertable into the coupling sleeve of the mold ejector plate. The coupling rod is tubular within which an axially displaceable actuating rod is provided, while the actuating rod has a conically tapered front end. By displacement of the actuating rod relative to the coupling rod, the radially engaging head region of the coupling rod is widened by radially outwardly directed forces. Thus, in a coupled condition, the head ends of the coupling rod and the actuating rod are connected in form-locked and force-locked manner with the coupling sleeve so that all coupling play is prevented. Additionally, the tubular coupling rod is radially divisible and is provided with an annular chamber in the radially divisible region. An annular piston which is axially movable in the annular chamber is also provided on the actuating rod. The '057 disclosure has nothing to do with injection molding of re-entrant surfaces in a polymeric component.
U.S. Pat. No. 5,882,568 to Kashiwagi discloses a method and molding machine for manufacturing shaped articles comprised of polymeric material. A molding machine for manufacturing a shaped article is comprised of a polymeric material and formed in a mold cavity between first and second mold halves of a mold assembly. At least one spring-loaded ejector member is provided in the first mold half and serves to eject the shaped article therefrom. The ejector member is movable toward and away from the second mold half and operates when the two mold halves are being opened. At least one resilient member urges the ejector member toward the second mold half. The resilient member exerts a resilient force to the ejector member, which is smaller than a tightening force of the mold halves. A method for manufacturing a shaped article comprised of a polymeric material includes providing at least one ejector member in the first mold half of the molding machine such that as the mold halves are opened, the ejector member urges the insulator away from the first mold half in which the ejector member is disposed. In one embodiment, the insulator is ejected by use of an ejection member having a distal end that is curved, thereby minimizing damage to the composite insulator. The method and molding machine is for manufacturing shaped articles comprised of polymeric material. This method is particularly suited for a composite electric insulator of fiber reinforced plastic coated with injection molded silicone or EPDM. Due to stickiness of the silicone and EPDM composition ejectors and resilient members are used to separate the molded composite article from the top and bottom sections of the mold. There are no re-entrant surfaces within the molded article and the method is unsuitable for releasing non flexible rigid molded article, such as an injection molded polymeric article.
U.S. patent application Ser. No. 2003/0113399 to Urbanek discloses a. two-plate injection molding machine. A two-plate injection molding machine comprising a movable mold mounting plate and a stationary mold mounting plate and at most three bars passing through the edge region of the mold mounting plates, wherein the closing force is applied to the movable mold mounting plate by pull bars, wherein at least two corner regions of the mold mounting plates have pull bars passing there through. The '399 patent discloses a two-plate injection molding machine. It uses two or four pull bars to close the mold and apply required forces during injection molding. The pull bars are placed at the corners of the molding plates thereby providing sufficient room there in between. There is no disclosure regarding molding re-entrant surfaces in this patent application.
U.S. patent application Ser. No. 2003/0147989 to Kasai et al. discloses a die clamping unit of an injection molding machine. A stationary platen and link housing are coupled to each other through tie bars. A movable platen is coupled to a front surface of the link housing through a toggle mechanism. Two slide bars are fixed to the back surface of the movable platen and each slide bar extends in a parallel way from a back surface toward the moving direction of the movable platen. Two hollow shafts are each fixed to the front surface of the link housing so as to correspond to the slide bar. Each hollow shaft extends in a parallel way from a front surface toward the moving direction of the movable platen. Each respective slide bar is inserted into the inside of the corresponding hollow shaft to allow it to slide along the inside of the hollow shaft. The die of the injection mold is opened or closed by a toggle mechanism driven by a servomotor. This die clamping mechanism has nothing to do with molding re-entrant surfaces in a polymeric molded article.
Foreign Publication No. JP2002172662 to Akimoto et al. discloses a method for manufacturing injection molded article. The mold is maintained at a temperature of polymer crystallization temperature ±20 C and is cooled to 70° C. or lower to produce polymeric molded parts with good appearance. This patent disclosure has nothing to do with injection molding polymeric articles with re-entrant surfaces.
Foreign Publication No. JP2003071876 to Asai et al. discloses a mounting structure of stamper for mold for injection molding. The slide bars are used to prevent movement of the stampers due to the thermal expansion caused by the heat of the polymer. This patent disclosure has nothing to do with injection molding polymeric articles with re-entrant surfaces.
Foreign Publication No. JP2009155926 to Kubo et al. discloses an injection mold. The stationary part of a mold has a variable diameter gate to allow for changing resin flow rate especially when a higher melt index polymer is used. As a result, the mold does not have to be re-created when the higher melt index polymer is used. This patent disclosure has nothing to do with injection molding polymeric articles with re-entrant surfaces.
Internet Publication. ‘Plastic Injection Moulding—An Introduction’ at http://www.azom.com/details.asp?ArticleID=265 provides an introduction to various aspects of polymeric injection molding practice. The Plastic Injection Moulding Internet Publication discloses common practices in plastic injection molding. No disclosure is contained in the article for injection molding of articles with re-entrant surfaces.
Internet Publication. ‘Injection Molded Tooling Specification’ at http://www.fordpkgstd.com/discus/messages/9/914.html?1064854717 discloses injection molded tooling specifications for the production of hand held containers and dunnage used in shipping containers for the shipment of automotive parts. No disclosure is contained in the article for injection molding of articles with re-entrant surfaces.
There remains a need in the art for a polymeric injection mold with retractable bars for producing re-entrant molded surfaces, wherein the re-entrant surfaces are in both sides of the parting line requiring retractable bars to be provided in both the stationary and the movable parts of the mold assembly.